SOAP is three different things
by Volker Weber
There are three major usage modes or ways to think about SOAP.
1. as a very generic messaging framework, as described in part one of the specification.
2. as a remote procedure call mechanism as in Part 2, Section 5.
2 a) An encoding for parameter values
2 b) A method calling syntax
3. as an extension mechanism for HTTP, as discussed in 6
Unfortunately, communication between developers or between customers and vendors is hampered by the different levels of interoperability implied by these different usage modes.